1. Field of the Invention
The present invention relates to a cyclonic combustion apparatus, and more particulary to a combustion apparatus that enables high specific heat release while producing exhaust gases with low concentrations of nitrogen oxide, commonly known as NO.sub.x, and of other exhaust gases such as carbon monoxide (CO).
2. Description of the Related Art
In the past, cyclone combustion chambers have been used to produce a cyclone of turbulent gases within a combustion chamber for combusting various solid materials, including poor quality coal and vegetable refuse. Such combustors are disclosed in "Combustion and Swirling Flows: A Review", N. Syred and J. M. Beer, Combustion and Flame, Volume 23, pages 143-201 (1974). A fluidized bed boiler having a cyclonic combustor is disclosed in U.S. Pat. No. 4,457,289 to Korenberg. These documents are incorporated by reference in this application. A fire tube boiler having a cyclonic combustor was commercially marketed by Cyclotherm Division, Oswego Package Boiler Co., Inc.
Although known adiabatic cyclone combustors provide high specific heat release, such known combustors have the disadvantage that combustion temperature is high and NO.sub.x emissions are high. In conventional cyclone combustors, combustion is unstable at low capacity burning and high turndown ratios are not possible in non-adiabatic combustors.
The turndown ratio of a combustion apparatus in a boiler is defined as the ratio of maximum load to minimum load and measures the ability of the boiler to operate over the extremes of its load ranges. A high turndown ratio allows for a wide range in the level of steam generation at a particular time. A wide range of steam generation is important to allow the boiler to most efficiently respond to varying steam demands.
Stable combustion can be achieved by not cooling the walls of a cyclone combustion chamber in the portion of the chamber into which air and fuel are injected for combustion, as is disclosed in U.S. patent application Ser. No. 928,096, filed Nov. 7, 1986 and assigned to a common assignee, which is incorporated by reference in this application. High wall temperatures near the chamber fuel and air entrance enable a high turndown ratio to be achieved. For example, by incorporating uncooled refractory lined walls at the air and fuel entrance to the combustion chamber, the turndown ratio can be increased from 4:1 up to and higher than 10:1. With such an arrangement, excess air over that required as a combustion reactant, can be decreased from 25-30% to about 5% and kept constant at about 5% over the turndown ratio of 10:1. In addition the flame temperature can be decreased from 3000.degree. F. for conventional fire tube boilers to about 2000.degree. F. By lowering the excess air and by lowering the flame temperature, NO.sub.x emission concentrations are lowered in the flue exhaust.
With pollution control requirements becoming constantly more stringent, it is necessary to decrease NO.sub.x emissions even further than is achieved with the combustion apparatus described above, while not increasing or while even decreasing the cost of the combustion equipment.
It is an object of the present invention to provide a cyclone combustion apparatus having a very high specific heat release, that can operate at relatively low combustion temperatures and with a relatively low percentage of excess air to produce low carbon monoxide emissions, commonly known as CO, and very low NO.sub.x emissions.
It is also an object of the invention to provide a cyclone combustion apparatus that enables stable combustion and a high turndown ratio and that does not require refractory lined walls at the entrance of the combustion chamber.
It is another object of the present invention to provide a cyclone combustion apparatus capable of stable combustion at relatively low flame temperatures that may be produced at a reduced cost.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advanatages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.